Experimental autoimmune uveitis (EAU) serves as a model for human autoimmune uveitis and for cell-mediated autoimmunity in general. EAU induced in mice by immunization with the retinal Ag interphotoreceptor retinoid-binding protein in CFA is driven by the Th17 response. Oral calcitriol (1,25-dihydroxyvitamin D3) prevented as well as partly reversed disease and suppressed immunological responses. In vitro, calcitriol directly suppressed IL-17 induction in purified naive CD4+ T cells without inhibiting Th17 lineage commitment, as reflected by unaltered RORγt, STAT3, and FoxP3 expression. In contrast, in vivo treatment with calcitriol of mice challenged for EAU impaired commitment to the Th17 lineage, as judged by reduction of both RORγt and IL-17 in CD4+ T cells. Innate immune response parameters in draining lymph nodes of treated mice were suppressed, as was production of IL-1, IL-6, TNF-α, and IL-12/IL-23p40, but not IL-10, by explanted splenic dendritic cells (DC). Finally, supernatants of calcitriol-conditioned bone marrow-derived DC had reduced ability to support Th17 polarization of naive CD4+ T cells in vitro and in vivo. Thus, calcitriol appears to suppress autoimmunity by inhibiting the Th17 response at several levels, including the ability of DC to support priming of Th17 cells, the ability of CD4+ T cells to commit to the Th17 lineage, and the ability of committed Th17 T cells to produce IL-17.

Induction of tissue-specific experimental autoimmune diseases involves an obligatory adjuvant effect to trigger an innate response of a type that will drive a Th1-biased adaptive response. This is achieved by use of CFA containing mycobacteria (Mycobacterium tuberculosis), whose recognition by cells of the innate immune system depends on TLRs that signal through the adaptor molecule MyD88. We examined the role of selected components of the MyD88 pathway in promoting experimental autoimmune uveitis (EAU). Mice deficient in MyD88, TLR2, TLR4, or TLR9 were immunized with the retinal Ag interphotoreceptor retinoid-binding protein in CFA, and their EAU scores and associated immunological responses were examined. MyD88−/− mice were completely resistant to EAU and had a profound defect in Th1, but not Th2, responses to autoantigen challenge. Surprisingly, TLR2−/−, TLR4−/−, and TLR9−/− mice were fully susceptible to EAU and had unaltered adaptive responses to interphotoreceptor retinoid-binding protein. Examination of IL-1R family members, which share the common adaptor MyD88 with the TLR family, revealed that IL-1R-deficient mice, but not IL-18-deficient mice, are resistant to EAU and have profoundly reduced Th1 and Th2 responses. These data are compatible with the interpretation that TLR9, TLR4, and TLR2 signaling is either not needed, or, more likely, redundant in the adjuvant effect needed to induce EAU. In contrast, signaling through the IL-1R plays a necessary and nonredundant role in EAU and can by itself account for the lack of EAU development in MyD88 mice.

Immunologically privileged retinal antigens can serve as targets of experimental autoimmune uveitis (EAU), a model for human uveitis. The tolerance status of susceptible strains, whose target antigen is not expressed in the thymus at detectable levels, is unclear. Here, we address this issue directly by analyzing the consequences of genetic deficiency versus sufficiency of a uveitogenic retinal antigen, interphotoreceptor retinoid-binding protein (IRBP). IRBP-knockout (KO) and wild-type (WT) mice on a highly EAU-susceptible background were challenged with IRBP. The KO mice had greatly elevated responses to IRBP, an altered recognition of IRBP epitopes, and their primed T cells induced exacerbated disease in WT recipients. Ultrasensitive immunohistochemical staining visualized sparse IRBP-positive cells, undetectable by conventional assays, in thymi of WT (but not of KO) mice. IRBP message was PCR amplified from these cells after microdissection. Thymus transplantation between KO and WT hosts demonstrated that this level of expression is functionally relevant and sets the threshold of immune (and autoimmune) reactivity. Namely, KO recipients of WT thymi generated reduced IRBP-specific responses, and WT recipients of KO thymi developed enhanced responses and a highly exacerbated disease. Repertoire culling and thymus-dependent CD25+ T cells were implicated in this effect. Thus, uveitis-susceptible individuals display a detectable and functionally significant tolerance to their target antigen, in which central mechanisms play a prominent role.

Susceptibility to experimental autoimmune uveitis (EAU), a model for human uveitis induced in mice with the retinal antigen interphotoreceptor retinoid-binding protein (IRBP), is controlled by “natural” CD4+CD25+ regulatory T (T reg) cells. To examine whether endogenous expression of IRBP is necessary to generate these T reg cells, we studied responses of IRBP knockout (KO) versus wild-type (WT) mice. Unexpectedly, not only WT but also IRBP KO mice immunized with a uveitogenic regimen of IRBP in complete Freund's adjuvant (CFA) exhibited CD25+ regulatory cells that could be depleted by PC61 treatment, which suppressed development of uveitogenic effector T cells and decreased immunological responses to IRBP. These EAU-relevant T reg cells were not IRBP specific, as their activity was not present in IRBP KO mice immunized with IRBP in incomplete Freund's adjuvant (IFA), lacking mycobacteria (whereas the same mice exhibited normal T reg cell activity to retinal arrestin in IFA). We propose that mycobacterial components in CFA activate T reg cells of other specificities to inhibit generation of IRBP-specific effector T cells in a bystander fashion, indicating that effective T reg cells can be antigen nonspecific. Our data also provide the first evidence that generation of specific T reg cells to a native autoantigen in a mouse with a diverse T cell repertoire requires a cognate interaction.

Invariant NKT cells (iNKT cells) have been reported to play a role not only in innate immunity but also to regulate several models of autoimmunity. Furthermore, iNKT cells are necessary for the generation of the prototypic eye-related immune regulatory phenomenon, anterior chamber associated immune deviation (ACAID). In this study, we explore the role of iNKT cells in regulation of autoimmunity to retina, using a model of experimental autoimmune uveitis (EAU) in mice immunized with a uveitogenic regimen of the retinal Ag, interphotoreceptor retinoid-binding protein. Natural strain-specific variation in iNKT number or induced genetic deficiencies in iNKT did not alter baseline susceptibility to EAU. However, iNKT function seemed to correlate with susceptibility and its pharmacological enhancement in vivo by treatment with iNKT TCR ligands at the time of uveitogenic immunization reproducibly ameliorated disease scores. Use of different iNKT TCR ligands revealed dependence on the elicited cytokine profile. Surprisingly, superior protection against EAU was achieved with α-C-GalCer, which induces a strong IFN-γ but only a weak IL-4 production by iNKT cells, in contrast to the ligands α-GalCer (both IFN-γ and IL-4) and OCH (primarily IL-4). The protective effect of α-C-GalCer was associated with a reduction of adaptive Ag-specific IFN-γ and IL-17 production and was negated by systemic neutralization of IFN-γ. These data suggest that pharmacological activation of iNKT cells protects from EAU at least in part by a mechanism involving innate production of IFN-γ and a consequent dampening of the Th1 as well as the Th17 effector responses.

ABSTRACT.Purpose: Management of uveitic cataract in patients with juvenile idiopathic arthritis (JIA) is challenging, and intraocular lens (IOL) implantation is controversial. This study investigated the outcome after minimally invasive surgery with IOL implantation. Methods: Retrospective analysis after phacoemulsification with in-the-bag IOL implantation was performed in 16 patients (17 operations) with ANA-positive JIAassociated chronic uveitis. In these patients, 25 G capsulectomy and anterior vitrectomy was performed and they received an intravitreal triamcinolone (TA) injection. Results: Mean age at uveitis onset was 5 ± 2 years, and surgery was performed at a mean age of 11 ± 2.2 years. Preoperatively, uveitis was inactive in all patients, and visual acuity was logMAR 0.8 ± 0.44; additional uveitis complications were present in all patients, and 15 patients were receiving systemic immunosuppression ⁄ biologicals. After surgery (mean follow-up 26.5 ± 11.7 months), presence of cystoid macular oedema, papilloedema, ocular hypertension ⁄ glaucoma and hypotony did not increase compared with baseline. There was no significant worsening of AC inflammation (by cell numbers and laser flare values). IOL deposits persisted in four patients, and synechiae developed in eight. The visual acuity was improved ( ‡2 lines) in all patients (mean logMAR 0.3 ± 0.24). Retrolental membrane formation was not noted. Secondary capsular opacification was observed in seven patients, requiring Nd:YAG capsulotomy in five of them. Conclusions: Phacoemulsification and in-the-bag IOL implantation may improve visual outcome in JIA-associated uveitis with minimally invasive surgical technique and intravitreal TA injection. Well-controlled uveitis with appropriate use of topical steroids and systemic immunosuppression or biologicals appears as a perioperative requirement.

Anterior uveitis was the most common anatomic site of intraocular inflammation. Using a tailored approach, screening for systemic etiologies is recommended, since 20% of all patients had associated systemic diseases.

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